1. Field of the Invention
The present invention relates to a system for attenuating the oscillations of a boom construction for an agricultural appliance, in particular for a field sprayer. In particular, the invention relates to an agricultural appliance with a boom construction that comprises a central portion which may, by means of a suspension device, be mounted on a support construction, such as a tool bar on a tractor or the like, which is arranged posteriorly of the boom construction, said suspension device comprising means that at least allow turning of the boom construction about an axis which is substantially perpendicular to the boom construction and which extends horizontally. "Posteriorly" is used herein to designate a support construction which is situated in a displaced parallel direction relative to the direction of advancement of the appliance.
2. Description of the Related Art
Usually agricultural appliances of this kind have a boom construction which is unsupported at its extremities in order to minimise the damage to the crops during the advancement of the agricultural appliance across a field by means of a tractor. Therefore the boom construction must be suspended on the tractor in a very specific manner, since it is necessary take into account that the suspension system of the boom construction must be able to absorb and attenuate the movements of the driving tractor so as to prevent them from being transmitted directly to the boom construction, and at the same time the system must ensure that the boom construction extends horizontally at any time, or alternatively at a given pitch. To this end the boom construction is usually suspended by means of a pendulum arm that extends perpendicularly to the longitudinal extent of the construction, and which is suspended in a centre of suspension which is somewhat above the centre of gravity of the boom construction whereby the boom construction will oscillate like a pendulum.
Examples of such suspension system are described in Swedish patent No. 421 853, French patent No. 1 564 543 and in British patent No. 2 028 078. "Power Farming", Vol. 56, No. 11, Nov. 1977, p. 57 also teaches a suspension system with a pair of bar elements ("C" in the photography) that extends in a vertical plane.
In order to provide a further bracing of the boom construction, it has been provided with a system of parallel rods which extend perpendicularly to the boom construction and in a horizontal plane, which rods are connected to the permanent tool bar on the tractor and the boom construction, respectively (cf. e.g. the above-cited British patent). When the boom construction turns, the bars will always extend in a mutually parallel manner and follow the boom construction when the latter turns.